Referring to FIG. 7, there is illustrated a conventional electric vacuum cleaner including dirt collection chamber 31 having a bottom surface and air inlet 32 tangentially provided on a side wall of dirt collection chamber 31. Cover 34 is provided to cover upper opening 33 of dirt collection chamber 31 and exhaust port 35 is formed in cover 34. Further, filter 36 is provided to cover upper opening 33 of dirt collection chamber 31. During an operation of electric blower 37, dirt particles are suctioned from suction nozzle 38 and travel into dirt collection chamber 31 via air inlet 32. The dirt particles in the suctioned dirt-laden air stream are centrifugally separated in dirt collection chamber 31, and the dirt-free air stream is exhausted through exhaust port 35 via filter 36 (see Japanese Patent Laid-open Publication No. 2001-104223).
Under such arrangement, however, the dirt particles collected in dirt collection chamber 31 via air inlet 32 adhere to filter 36, resulting in a significant disturbance of the suction flow, which in turn significantly reduces the overall suction force. In an attempt to solve such problem, filter 36 of an enlarged filtering area has been tried. However, such enlarged filter entails a problem of increasing the size of dirt collection chamber 31 and consequently increasing the overall size of the vacuum cleaner itself.